HPLC analysis of the phenylisothiocyanate (PITC) derivatives of taurine from physiologic samples.

Taurine is the major free intracellular amino acid. It has become the focus of study by many as a conjugator of bile and as a neurotransmitter and intracellular messenger. In this report we document a technique for measuring taurine in physiologic samples which is rapid, reproducible, and accurate. Any physiologic sample is first derivatized with phenylisothiocyanate (PITC) and separated by reverse phase HPLC, and then taurine is detected by UV at 254 nm. The advantages of this technique for the measurement of taurine are accuracy, small sample size, and reproducibility, and with an automated system many samples can be analyzed.

Free amino acids and calcium, magnesium and zinc levels in Friedreich's ataxia.

Free amino acid levels and zinc, magnesium and calcium content have been determined in autopsy samples of 9 areas of the brain, two skeletal muscles, and the right ventricle, left ventricle and septum of the heart of a Friedreich's ataxia subject.

Subcellular distribution of neuroactive amino acids in brains of genetically epileptic rats.

The subcellular distribution of amino acids was compared in brains of genetically seizure-susceptible (SS) and genetically seizure-resistant (SR) rats. The total taurine content (mumol/brain) in the P2B, or synaptosomal, fraction in SS rats was only 37% of that of SR rats. Glutamate, glutamine, glycine, alanine, and gamma-aminobutyric acid (GABA) contents were unaltered. No alterations in total content were found in other subcellular fractions for the amino acids studied. SS animals that had never been stimulated to audiogenic seizure had decreased concentrations of taurine (nmol/mg protein) in the P2, P2B, and P2C fractions as compared with SR animals. These fractions contain crude synaptosomes, enriched synaptosomes, and enriched mitochondria, respectively. Phosphoethanolamine concentrations were also decreased in the P2B fractions, but concentrations of other amino acids were unaltered, as compared with SR animals. Twenty-four hours after the intracerebroventricular injection of taurine (6 mumol) in SS animals that had never been convulsed, taurine concentrations were significantly increased in whole brain homogenate and P2 and P2B fractions as compared with SS animals not given taurine. This treatment left unaltered the concentrations of glutamate, glutamine, GABA, and glycine in brain homogenate and P2 fraction. Because decreases in taurine concentration were seen in animals that had not been convulsed, these alterations are intrinsic to the SS strain and are not a consequence of convulsive activity. In view of the antiepileptic action of taurine, and the fact that an impairment of taurine transport in the brain of SS rats had previously been demonstrated, we suggest that a defect in the biochemistry of taurine is partially responsible for the seizure susceptibility of the SS rat.

Relative contribution of the mother, the nurse and endogenous synthesis to the taurine content of the newborn and suckling rat.

The relative contributions have been determined of taurine derived from the mother in utero, via milk during nursing, and from endogenous biosynthesis to the total taurine content of the rat pup between birth and weaning. At birth, 32% of the taurine in the pup has been biosynthesized, and this proportion rises to 83% by day 20 of life. At birth, 67% has been derived from the mother in utero, and by day 20 this has fallen to 4% of the total. This maternal taurine is lost with a half-life of 16 days. There is wide variation in the turnover from different tissues, the pancreas having a half-life of 7 days, and the brain 50 days. However, the amount of maternal taurine in the brain actually increases by 38% over the first 8 days of life. By day 20, 13% of the taurine content of the pup has been obtained from the milk. Taurine turnover in the suckling pup differs from turnover after weaning in that wholebody turnover from the suckling rat is not slower than exchange between organs. In other words, tissues are not in kinetic equilibrium. After animals are weaned, regardless of the taurine content of the diet, taurine is interchanged between organs faster than it is excreted from the animal.

Epilepsy and the concentrations of plasma amino acids in humans.

We have examined the correlation between the presence of epilepsy in humans, and plasma amino acid levels. Subjects were divided into those having pure generalized tonic-clonic seizures (grand mal group), those having generalized tonic-clonic seizures plus other types of epilepsy (mixed group), and those suffering from epilepsies other than grand mal (no grand mal group). Compared to non-epileptic controls, the grand mal group had significantly higher fasting plasma levels of aspartate (100% increase) and glutamate (380% increase) but significant decreases were seen with phenylalanine (?23%), lysine (?27%), and tryptophan (?30%). The no grand mal group showed similar changes except for lysine. The mixed group showed elevations in glutamate, but decreases only in cysteine and methionine. In response to a high protein meal, plasma levels of alanine, cysteine and methionine rose significantly less for the no grand mal group compared to the control group. Increases in aspartate and glutamate concentrations strongly correlated with the prescription of phenytoin. However, the concentrations of these amino acids were not significantly correlated with the actual plasma levels of phenytoin.

Diet and biosynthesis as sources of taurine in the mouse.

The quantitative importance of diet versus biosynthesis as sources of taurine has been established in mice receiving dietary levels of 0.062% [3H]taurine and 0.74% [35S]methionine as sole sulfur-containing amino acids. After 15 days on diets radiolabeled with these levels of taurine and methionine, 16% of total-body taurine had been derived from diet and 24% from biosynthesis. By 30 days, these contributions had risen to 29% and 33%, respectively, and by 61 days to 46%. The half-life of turnover of taurine in the mouse was 18.6 days. These findings indicate that, like the rat and guinea pig, but unlike the cat and human, the mouse exhibits considerable biosynthetic capacity for taurine.

Relative contribution of diet and biosynthesis to the taurine content of the adult rat.

The relative contribution of diet and biosynthesis to the taurine content of the rat has been determined quantitatively under various dietary conditions. Rats were maintained on diets containing [3H]taurine and/or [35S]methionine of known amounts and specific activities, and subsequently the specific activity of taurine in various tissues was determined. This approach gives a quantitative measure of how much taurine is biosynthesized versus how much is derived from the diet regardless of the biosynthetic route or site of biosynthesis in the animal. With no taurine in the diet, over an 87-day period, 54% of the taurine in the animal had been biosynthesized. This fell to 29% if taurine was present in the diet, and the contribution of dietary taurine to body pools rose to 58%. These changes in biosynthetic contributions were not accompanied by an alteration in the rate of biosynthesis but by an alteration in rate of excretion. When the amounts of biosynthesized taurine appearing in the urine over 63 days was added to the amounts found in the carcass, 3.1 mmol were found to be biosynthesized by animals receiving taurine in the diet as compared to 2.9 mmol in animals on a taurine-deficient diet. In any one experiment, the contribution of diet or biosynthesis is invariant from tissue to tissue indicating that the rate of exchange of taurine between tissues is faster than the rate of elimination of taurine from the body.